There are several ways that the party squeezes life out of its citizens. One is through its constant monitoring of party members. Wherever these members go, they know that they are being watched, surveilled, monitored and analyzed. If there ever was a way to stifle true creativity, life and emotion, that's going to be it. The monitors, which lead to the Thought Police and imprisonment for Thoughtcrimes, are a way for the party to be in every aspect of your life, even in your sleep. Instead of being spontaneous and happy, you have to worry that what you are saying and doing will be misinterpreted, and considered a crime. Fear rules, and there is no escape from it, even in the comfort of your own home.
Another way that they repress life is through resource withholdings. They declare constant rationing for the war effort; this keeps the population underfed on lousy food, and keeps their housing and quality of living at a very depressing level. It's hard to get excited about breaks and eating when the food stinks. It's hard to feel comfortable and rested when your apartment is falling apart and cold. They keep the people living in a constant state of unease and discomfort in regards to their physical circumstances, and that makes it hard to live a happy and fulfilled life.
Another way that they depress life and its joys is by taking away any pleasure or happiness in human relationships. They train their young women to detest men and sex, and to find any source of intimacy to be an dirty, awful thing that must be endured in order to keep the race going. They discourage love in marriages, and friendships in general. All warmth, friendliness, love, sex and intimacy is discouraged and looked down upon, even brainwashed out of their citizens. Winston is particularly impacted by this--he is lonely, friendless, without family, a survivor of a loveless marraige, and without any real relationships in his life. It makes his life empty and worthless. The party plays into that and channels all of that energy that would be put into relationships into party fervor and patriotism instead.
Those are just a few ways that the party drains life from its citizens; I hope that helped!
Other people may have other opinions, but in my opinion, the Party does this by controlling everything the members of the society do. By controlling them in so many ways, the Party essentially takes away their lives and their individuality.
I think the Party does this in a variety of ways. It watches people all the time to make sure they are not committing thought crime. It tries to take away all of their emotions (like romantic love). Then it tries to give them other "government issue" emotions (Two-Minutes Hate).
In these ways, the Party takes what is human and alive out of its people.